1. Field of the Invention
There is a continuing need for improved assay methods for the detection of an analyte in a sample. The analyte generally is a member of a specific binding pair consisting of ligand and its homologous receptor. Exemplary of sbp members are antigens and antibodies.
The mammalian red blood cells carry numerous antigens some of which must be accurately identified in both patient and donor for medical procedures such as transfusions. Accurate determination of blood groups, A, B, AB, O and D (Rh.sub.o) is critically important. Also antibodies present in the blood to such antigens can be of diagnostic interest.
Conventionally, agglutination techniques are used on a microscope slide or in a tube. Improved rapid accurate screening of blood is desirable in view of the large numbers of samples which must be tested.
2. Description of the Prior Art
Identification of red blood cell antigens by agglutination techniques is standard, e.g., C. Hudson and F. C. Hay, Practical Immunology, Second Edition, Blackwell Scientific Publications, Oxford (1980), p. 139. U.S. Pat. No. 3,862,303 is exemplary of immunologial detection and identification of serological factors using carrier particles such as latex beads. Smith, FEBS Letters 77,25 (1977) describes a fluorescent immunoassay.
U.S. patent application Ser. No. 434,761, filed Oct. 15, 1982, now U.S. Pat. No. 4,550,017 concerns Fluorescence Screening for Blood Typing.
The use of laser beams and slits to differentiate particles based on their relative size by the correlation of fluorescence fluctuations in a relatively large sample volume is described by Briggs et al, Science, 212: 1266-1267, 1981, and by Nicoli et al., Proc. Natl. Acad. Sci., USA, 77: 4904-4908, 1980.
Various squarate dyes are discussed by Sprenger, et al., Angew. Chem., 80, 541 (1968) [Angew. Chem. Internatl. Edit, Vol. 7: 530-535, 1968]; Sprenger, et al., Angew. Chem., 79; 581, 1967 [Angew. Chem. Internatl. Edit, Vol. 6: 553-554, 1967]; Sprenger, et al., Angew. Chem. internat. Edit, 5: 894, 1966; and Maahs, et al., ibid., 5: 888, 1966.
The employment of a merocyanine dye for the detection of malignant leukocyte cells is described in U.S. Pat. No. 4,424,201.
U.S. Pat. No. 3,853,987 discloses an immunological reagent and radioimmunoassay. In a preferred method for detecting clumping of his reagents, the patentee dilutes a suspension of the reaction mixture and passes it through a flow cell in a spectrophotofluorometer.